Sadao Higuchi

Fabrications of cerium-substituted YIG thin films for magnetic field sensor by pulsed-laser deposition

We described the pulsed-laser deposition (PLD) and characterization of cerium doped yttrium iron garnet (Ce:YIG, Ce/sub 0.6/Y/sub 2.4/Fe/sub 5/O/sub 12/) thin films for magnetic field sensor applications. It was found that crystallized Ce:YIG films were obtained by the deposition at 900/spl deg/C substrate temperature and in 10 mtorr argon or oxygen ambient gas. The Faraday rotation angle was very large; 4.2 deg//spl mu/m at 430 nm wavelengths. The charge state control of cerium was important for the crystallinity and high Faraday rotation. The lower temperature or higher ambient gas pressure controlled the cerium charge state Ce/sup 4+/, because the oxygen and cerium released from an ablated target accelerated to form cerium oxide, the thin film was noncrystalline and no Faraday rotation occurred.

Magneto-Optical Properties of Cerium-Substituted Yttrium Iron Garnet Single Crystals Grown by Traveling Solvent Floating Zone Method

A cerium-substituted yttrium iron garnet (Y3-xCexFe5O12) single crystal was grown by the traveling solvent floating zone (TSFZ) method in an oxygen environment. Using a Fe- and Ce-rich solvent, high quality single crystals with smooth and lustrous surface were grown at a rate of 1.0 mm/h. The segregation coefficient of Ce was calculated approximately as 0.2 from the compositional profile in the grown crystals measured by electron probe X-ray microanalyzer (EPMA). The optical absorption coefficient and the Faraday rotation angle of Y2.82Ce0.18Fe5O12 at 1550 nm wavelength were 0.12 cm-1 and -740 deg/cm, respectively. The figure of merit of a Faraday rotator was 1423 deg/dB. The absorption loss and sensitivity of the same Y2.82Ce0.18Fe5O12 (d=0.6 mm) for the magnetic field sensor were 0.03 dB and 0.1%/Oe, respectively, at 1550 nm wavelength. These results suggest that cerium-substituted yttrium iron garnet is a high performance material for the Faraday rotator at 1550 nm wavelength.

Pulsed-Laser Deposition of LiNbO3 in Low Gas Pressure Using Pure Ozone

Pulsed-laser deposition (PLD) growth of stoichiometric LiNbO3 has been investigated in detail in the low gas pressure region where the mean free path of ablated species is longer than the target-to-substrate distance. We have found that the reduction of gas pressure effectively suppresses Li deficiency, and therefore, is a promising way of overcoming the nonstoichiometory problem that has been inherent to the conventional PLD growth of LiNbO3. In such low-pressure growth, we have found that ozone atmosphere is more favorable than that of molecular oxygen, because the crystallographic quality and surface flatness is better in films grown with ozone than in those grown with molecular oxygen. These results open the way to nanoscale lattice engineering of Li-containing oxide materials.

Magnetic field sensors using Ce:YIG single crystals as a Faraday element

Magnetic field sensors based on creation of the Faraday effect by rotation magnetization in Ce:YIG crystals are studied. The large linear magnetic birefringence (LMB) of /spl Delta/n=-1.7/spl times/10/sup -4/ was observed in the Ce/sub 0.18/Y/sub 2.82/Fe/sub 5/O/sub 12/ crystal and it was found from both the calculation and experimental investigations that the LMB affects the linearity of the sensor output. The validity of the method of utilizing a pair of Ce:YIG crystals with an azimuthal angle of 90 deg in the optical axis is demonstrated as a method of improving these phenomena.

Pulsed-Laser Deposition of LiNbO3 Thin Films at Low Oxidation Gas Pressure with Pure Ozone

The pulsed-laser deposition growth of LiNbO3 thin films is carried out using a stoichiometric polycrystalline target in an ozone atmosphere. Reducing the gas pressure to 5×10-3 Pa is found to be effective for suppressing the appearance of a Li-deficient phase in the films. Consequently, the chemical composition of the film prepared at an optimum substrate temperature of 550°C is close to stoichiometric values, which indicates that the long mean free paths of Li and Nb are a key issue in the control of the stoichiometry of LiNbO3 thin films. Moreover, the obtained films show a sufficiently high optical absorption edge of 4.19 eV, which is 0.24 eV higher than that of a stoichiometric LiNbO3 single crystal.

Characteristics of Bi:YIG Magneto-Optic Thin Films Fabricated by Pulsed Laser Deposition Method for an Optical Current Transformer

Pulsed laser deposition (PLD) technique is applied for fabricating Bi doped yttrium iron garnet (BixY3-xFe5O12) (Bi:YIG) thin films which can be used for optical current transformer. Growth conditions of high quality Bi:YIG thin films on Gd3Ga5O12 (GGG) substrates are investigated by varying PLD process parameters. The magneto-optic sensitivity coefficient of the fabricated Bi-YIG thin film is measured as 44 deg/T at a wavelength of 500 nm.

Fabrications of optically functional thin films for electric and magnetic field sensors by pulsed laser deposition

We describe the pulsed-laser deposition and characteristics of bismuth silicon oxide (BSO, Bi12SiO20) thin films and Ce-doped yttrium iron garnet (Ce:YIG, CexY3-xFe5O12) thin films for the electric and magnetic field sensor application. It was found that BSO films deposited on yttria-stabilized zirconia substrates heated at 400 degree(s)C or higher in an oxygen ambient gas were crystallized and the (310) plane was perpendicular to the substrate normal. The highly (310) oriented crystallized films were also deposited even on SiO2 glass substrates. On the other hand, crystallized Ce:YIG films were obtained by the deposition in an Ar ambient gas, and not in an oxygen ambient gas, indicating the importance of the control of the charge state of Ce ions. The magneto-optic data of Ce:YIG films are also reported.

Fabrication of Ce:YIG film for electric and magnetic field sensor by pulsed-laser deposition and laser-induced forward transfer

Ce-doped yttrium iron garnet (Ce:YIG) thin films were deposited for the first time by pulsed-laser deposition (PLD) on gadolinium gallium garnet (GGG(111)) substrates. Well crystallized film was obtained at high substrate temperature (approximately 900 degree(s)C) and in low Ar gas pressure (approximately 50 mtorr). A Faraday rotation angle was wavelength dependent, and the largest value was 4.2 x 104 deg/cm at 420 nm. The control of the charge state of Ce ion is necessary for crystallization. The deposited Ce:YIG films were transferred by laser-induced forward transfer (LIFT) process to obtain a thick film.

Fabrication of Ce:YIG film with different composition by pulsed-laser deposition

Ce-doped yttrium iron garnet (Ce:YIG) with different compositions of Y2CeFe5O12, Y2CeFe4.25Ga0.75O12, Y1.6Gd0.4CeFe5O12 were deposited by PLD on GGG(111) SUBSTRATE. The crystallinity, transmittance and surface morphology were observed for the films deposited at different depositions conditions of argon or oxygen gas pressures and substrate temperatures.

Study of Optical Magnetic Field Sensor Using Cerium-Substituted Yttrium Iron Garnet Single Crystal

The linear magnetic birefringence (LMB) in Ce-substituted Y3Fe5O12 crystals grown by the floating zone method and its influence on the characteristics of optical magnetic field sensors were studied. It was found that the measured LMB values of Δn001=-1.2×10-4 and Δn111=-1.7×10-4 in the Ce0.17Y2.83Fe5O12 sample were three times as large as those in YIG. The influence of LMB on the linearity of the magnetic field sensor, which was based on the Faraday effect created by magnetization rotation, was estimated quantitatively from the analytical result obtained by the Jones matrix calculation method. It was found from both calculation and experimental investigations that LMB strongly affects the linearity of the sensor output. It was successfully demonstrated that use of a pair of Ce:YIG crystals was very effective in improving the sensitivity of the sensor output.